Heavy quark spin symmetry and heavy baryons: electroweak decays

2010

Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b->c semileptonic decays of these hadrons.

$\bar B_s\to K$ semileptonic decay from an Omn\`es improved constituent quark model

2014

We study the $f^+$ form factor for the semileptonic $\bar B_s\to K^+\ell^-\bar\nu_\ell$ decay in a constituent quark model. The valence quark estimate is supplemented with the contribution from the $\bar B^*$ pole that dominates the high $q^2$ region. We use a multiply-subtracted Omn\`es dispersion relation to extend the quark model predictions from its region of applicability near $q^2_{\rm max}=(M_{B_s}-M_K)^2\sim 23.75$ GeV$^2$ to all $q^2$ values accessible in the physical decay. To better constrain the dependence of $f^+$ on $q^2$, we fit the subtraction constants to a combined input from previous light cone sum rule [Phys. Rev. D 78 (2008) 054015] and the present quark model results. …

$B\to ��$ semileptonic decays and $|V_{ub}|$

2014

We reevaluate the $B\to��\,l^+��_l$ decay width as a full $B\to����\,l^+��_l$ four-particle decay, in which the two final pions are produced via an intermediate $��$ meson. The decay width can be written as a convolution of the $B\to��\,l^+��_l$ decay width, for an off-shell $��$, with the $��\to����$ line shape. This allows to fully incorporate the effects of the finite $��$ meson width. As shown, consideration of the $��$ meson width effects increase the $|V_{ub}|$ value by some 8%, rendering it in better agreement with the determination based in the $B\to��$ decay. We take the $q^2$ dependence of the $B\to ��$ semileptonic form factors from a dispersive Omn��s representation. The Omn��s …

B¯s→K semileptonic decay from an Omnès improved constituent quark model

2014

We study the f+ form factor for the semileptonic B¯s→K+ℓ−ν¯ℓ decay in a constituent quark model. The valence quark estimate is supplemented with the contribution from the B¯⁎ pole that dominates the high q2 region. We use a multiply-subtracted Omnès dispersion relation to extend the quark model predictions from its region of applicability near qmax2=(MBs−MK)2∼23.75 GeV2 to all q2 values accessible in the physical decay. To better constrain the dependence of f+ on q2 , we fit the subtraction constants to a combined input from previous light cone sum rule by Duplancic and Melic (2008) [11] and the present quark model results. From this analysis, we obtain Γ(B¯s→K+ℓ∅

Pionic decay of Lambda Hypernuclei in a Continuum Shell Model

2002

We evaluate pionic decay widths of Lambda hypernuclei using a shell model for, both the nuclear bound and the continuum nucleon wave functions in the final state, and distorted waves for the outgoing pion. An excellent agreement with the recent KEK measurement of $\pi^-$-decay widths of $^{12}_\Lambda$C and $^{28}_\Lambda$Si is found. Besides, results for $^{56}_\Lambda$Fe are consistent with the existing upper bound.

A Heavy Quark Symmetry Approach to Baryons

2005

We evaluate different properties of baryons with a heavy c or b quark. The use of Heavy Quark Symmetry (HQS) provides with an important simplification of the non relativistic three body problem which can be solved by means of a simple variational approach. This scheme is able to reproduce previous results obtained with more involved Faddeev calculations. The resulting wave functions are parametrized in a simple manner, and can be used to calculate further observables.

Semileptonic B ->pi decays from an Omnes improved nonrelativistic constituent quark model

2005

The semileptonic $B\to \pi l^+ \nu_l$ decay is studied starting from a simple quark model which includes the influence of the $B^*$ pole. To extend the predictions of a nonrelativistic constituent quark model from its region of applicability near $q^2_{\rm max}=(m_B-m_\pi)^2$ to all $q^2$ values accessible in the physical decay, we use a novel multiply-subtracted Omn\`es dispersion relation, which considerably diminishes the form factor dependence on the elastic $\pi B \to \pi B$ scattering amplitudes at high energies. By comparison to the experimental branching fraction we extract $|V_{ub}| = 0.0034 \pm 0.0003 ({\rm exp}) \pm 0.0007 ({\rm theory})$. To further test our framework, we also s…

Hyperfine mixing in b -> c semileptonic decay of doubly heavy baryons

2010

We qualitatively corroborate the results of [W. Roberts, M. Pervin, Int. J. Mod. Phys. A 24 (2009) 2401] according to which hyperfine mixing greatly affects the decay widths of b -> c semileptonic decays involving doubly heavy bc baryons. However, our predictions for the decay widths of the unmixed states differ from those reported in the work of Roberts and Pervin by a factor of 2, and this discrepancy translates to the mixed case. We further show that the predictions of heavy quark spin symmetry, might be used in the future to experimentally extract information on the admixtures in the actual physical bc baryons, in a model independent manner.

A nonrelativistic quark model evaluation of exclusive $b\to c$ semileptonic decay of triply heavy baryons and $c\to s,d$ semileptonic decay of $cb$ b…

2013

We present results for exclusive $b\to c$ semileptonic decays of ground state triply-heavy baryons and for semileptonic $c\to s,d$ decays of doubly heavy ground state $cb$ baryons. In both cases, we have derived for the first time heavy quark spin symmetry relations for the hadronic amplitudes near zero recoil. Though strictly valid in the limit of very large heavy quark masses and near zero recoil, they turn out to be reasonable accurate for the whole available phase space in these decays and for the actual heavy quark masses we use. With these relations we have made approximate, but model independent, predictions for ratios of decay widths. In the case of spin-1/2 $cb$ baryons, we find th…

Charmed and Bottom Baryons: a Variational Approach based on Heavy Quark Symmetry

2003

The use of Heavy Quark Symmetry to study bottom and charmed baryons leads to important simplifications of the non-relativistic three body problem, which turns out to be easily solved by a simple variational ansatz. Our simple scheme reproduces previous results (baryon masses, charge and mass radii, $...$) obtained by solving the Faddeev equations with simple non-relativistic quark--quark potentials, adjusted to the light and heavy--light meson spectra. Wave functions, parameterized in a simple manner, are also given and thus they can be easily used to compute further observables. Our method has been also used to find the predictions for strangeness-less baryons of the SU(2) chirally inspire…

Study of the semileptonic decays B→π, D→π and D→K

2006

The semileptonic decay B->pi is studied starting from a simple quark model that takes into account the effect of the B* resonance. A novel, multiply subtracted, Omnes dispersion relation has been implemented to extend the predictions of the quark model to all q^2 values accesible in the physical decay. By comparison to the experimental data, we extract |V_ub|=0.0034 +/- 0.0003(exp.) +/- 0.0007(theory). As a further test of the model, we have also studied D->pi and D->K decays for which we get good agreement with experiment.

Exclusive $c\to s,d$ semileptonic decays of ground-state spin-1/2 doubly charmed baryons

2011

We evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons driven by a $c\to s,d$ transition at the quark level. Our results for the form factors are consistent with heavy quark spin symmetry constraints which are valid in the limit of an infinitely massive charm quark and near zero recoil. Only a few exclusive semileptonic decay channels have been theoretically analyzed before. For those cases we find that our results are in a reasonable agreement with previous calculations.

Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

2006

We evaluate static properties and semileptonic decays for the ground state of doubly heavy $\Xi, \Xi', \Xi^*$ and $\Omega, \Omega', \Omega^*$ baryons. Working in the framework of a nonrelativistic quark model, we solve the three--body problem by means of a variational ansazt made possible by heavy quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one--gluon exchange. Our results for static properties (masses, charge and mass radii, magnetic moments...) are, with a few exceptions for the magnetic moments, in good agreemen…

Exclusive c → s, d Semileptonic Decays of Spin-1/2 and Spin-3/2 cb Baryons

2013

We present results for exclusive semileptonic decay widths of ground state spin-$1/2$ and spin-$3/2$ $cb$ baryons corresponding to a $c\to s, d$ transition at the quark level. The relevance of hyperfine mixing in spin-1/2 $cb$ baryons is shown. Our form factors are compatible with heavy quark spin symmetry constraints obtained in the infinite heavy quark mass limit.

$B\to \rho$ semileptonic decays and $|V_{ub}|$

2014

We reevaluate the $B\to\rho\,l^+\nu_l$ decay width as a full $B\to\pi\pi\,l^+\nu_l$ four-particle decay, in which the two final pions are produced via an intermediate $\rho$ meson. The decay width can be written as a convolution of the $B\to\rho\,l^+\nu_l$ decay width, for an off-shell $\rho$, with the $\rho\to\pi\pi$ line shape. This allows to fully incorporate the effects of the finite $\rho$ meson width. As shown, consideration of the $\rho$ meson width effects increase the $|V_{ub}|$ value by some 8%, rendering it in better agreement with the determination based in the $B\to\pi$ decay. We take the $q^2$ dependence of the $B\to \rho$ semileptonic form factors from a dispersive Omn\`es re…

Exclusive c→s,d semileptonic decays of ground-state spin-1/2 doubly charmed baryons

AbstractWe evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons driven by a c→s,d transition at the quark level. Our results for the form factors are consistent with heavy quark spin symmetry constraints which are valid in the limit of an infinitely massive charm quark and near zero recoil. Only a few exclusive semileptonic decay channels have been theoretically analyzed before. For those cases we find that our results are in a reasonable agreement with previous calculations.

Doubly heavy quark baryon spectroscopy and semileptonic decay

2006

Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground state of doubly heavy $\Xi$ and $\Omega$ baryons. We solve the three-body problem using a variational ansatz made possible by the constraints imposed by heavy quark spin symmetry. In order to check the dependence of our resultson the inter-quark interaction we have used five different quarkquark potentials which include Coulomb and hyperfine terms coming fromone-gluon exchange, plus a confining term. Our results for the spectra are in good agreement with a previous calculation done using a Faddeev approach. For the semileptonic decay our results for the total decay …

Exclusive $c\to s,d$ semileptonic decays of ground-state spin-1/2 and spin-3/2 doubly heavy $cb$ baryons

2012

We evaluate exclusive semileptonic decays of ground-state spin-1/2 and spin-3/2 doubly heavy $cb$ baryons driven by a $c\to s,d$ transition at the quark level. We check our results for the form factors against heavy quark spin symmetry constraints obtained in the limit of very large heavy quark masses and near zero recoil. Based on those constraints we make model independent, though approximate, predictions for ratios of decay widths.

Hyperfine mixing in electromagnetic decay of doubly heavy bc baryons

2010

We investigate the role of hyperfine mixing in the electromagnetic decay of ground state doubly heavy bc baryons. As in the case of a previous calculation on b -> c semileptonic decays of doubly heavy baryons, we find large corrections to the electromagnetic decay widths due to this mixing. Contrary to the weak case just mentioned, we find here that one cannot use electromagnetic width relations obtained in the infinite heavy quark mass limit to experimentally extract information on the admixtures in a model independent way.

The effect of hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons

2010

We consider the role played by hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons, which give rise to large corrections to the decay widths in both cases.

Heavy sterile neutrinos in stellar core-collapse

2018

We perform spherically symmetric simulations of the core collapse of a single progenitor star of zero age main sequence mass $M_{\rm ZAMS} = 15 \, M_{\odot}$ with two models of heavy sterile neutrinos in the mass range of hundred MeV$/c^2$. According to both models, these hypothetical particles are copiously produced in the center, stream outwards a subsequently decay releasing energy into final states (including neutrinos) of the Standard Model. We find that they can lead to a successful explosion in otherwise non-exploding progenitors. Depending on their unknown parameters (e.g., mass and coupling constants with matter), we obtain either no explosion or an explosion of one of two types, i…

Exclusive semileptonic decays of ground-state $cb$ baryons driven by a $c\to s,d$ quark transition

2012

We evaluate semileptonic decays of spin-1/2 and spin-3/2 doubly heavy $cb$ baryons. The decays are driven by a $c\to s,d$ transition at the quark level. We check our results for the form factors against heavy quark spin symmetry constraints obtained in the limit of very large heavy quark masses and near zero recoil.

Semileptonic decays of spin-1/2 doubly charmed baryons

2012

We evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons. The decays are driven by a $c\to s,d$ transition at the quark level. Our form factors are consistent with Heavy Quark Symmetry constraints. The latter are valid in the limit of infinitely heavy quark mass at zero recoil.

B→ρsemileptonic decays and|Vub|

2014

We reevaluate the $B\to\rho\,l^+\nu_l$ decay width as a full $B\to\pi\pi\,l^+\nu_l$ four-particle decay, in which the two final pions are produced via an intermediate $\rho$ meson. The decay width can be written as a convolution of the $B\to\rho\,l^+\nu_l$ decay width, for an off-shell $\rho$, with the $\rho\to\pi\pi$ line shape. This allows to fully incorporate the effects of the finite $\rho$ meson width. As shown, consideration of the $\rho$ meson width effects increase the $|V_{ub}|$ value by some 8%, rendering it in better agreement with the determination based in the $B\to\pi$ decay. We take the $q^2$ dependence of the $B\to \rho$ semileptonic form factors from a dispersive Omn\`es re…

$\bar B_s\to K$ semileptonic decay from an Omn\`es improved nonrelativistic quark model

2014

We study the $f^+$ form factor for the $\bar B_s\to K^+\ell^-\bar\nu_\ell$ semileptonic decay in a nonrelativistic quark model. The valence quark contribution is supplemented with a $\bar B^*$-pole term that dominates the high $q^2$ region. To extend the quark model predictions from its region of applicability near $q^2_{\rm max}=(M_{B_s}-M_K)^2$, we use a multiply-subtracted Omn\`es dispersion relation. We fit the subtraction constants to a combined input from previous light cone sum rule results in the low $q^2$ region and the quark model results (valence plus $\bar B^*$-pole) in the high $q^2$ region. From this analysis, we obtain $\Gamma(\bar B_s\to K^+\ell^-\bar\nu_\ell)=(5.47^{+0.54}_…